I have installed a 16kW standby generator and I am having a problem with the furnace. It is a 10kW furnace and the rest of the generatoris running lights, outlets and a well pump. When the generator starts, everything is fine. Then about five minutes with the generator running, it trips the 65 Amp breaker inside the generator housing. I can run the lights, outlets and well pump by itself with no problem, but can't run the furnace without shutting down the generator. The furnace is 240V on a 50A 2 pole breaker. It will not trip this breaker. The generator main is a 70A breaker. This is the third one I have installed. The other two have no problems. Could the 65A breaker be faulty? Please help. Thanks, I have been looking at different questions on this site, and I have liked what I have seen so far.

On 10 kw electric heating elements you will pull around 40 amps not including the starting amps of the blower. Are you shuting off the compressor on the heat pump while trying to run the heat? If not this may be your problem. What size is your wire service? If its to small the voltage will drop with the load and in turn the amp draw will rise.

As far as I know this is only a furnace. I do not think it is a heat pump. It is installed inside the house with no external attachments. The wire running from the generator to the dist. box (auto changeover) is #6. The wire is running about 100 ft. from the generator to the new dist. box. I will check amps on that wire to see if I have a voltage drop problem, but I think it should be OK. (this is not my gen. I installed it for someone else at their residence) Thank you for your reply T-Top.

You need to check the full load amps of every thing running to see if your generator will handel the load. Starting amps and running amps are to different things when using a generator.

Starting amps would have ahigher demand on the system than running amps, wouldn't it? It will start with everything OK, then about 5 minute later it trips the 65A breaker at the gen. I am going to look at it on Mon. (it is not mine I installled it for someone else at their home). I am going to take full readings (amps nl fl, voltages, etc... ) I don't notice the generator having a strain on the system w/ or w/o the furnace on line. It sounds the same running. Thanks again for your help T-Top. Will post readings on Mon.

Listening to many posts on furnace operation, there has been some attention to erratic operation of furnaces with inverters/generators due to no ground. You might check grounding and/or the ground/neutral bonds. I'm silently wondering whether a ground rod should be, or can be, used at the generator to equalize the ground potentials oor if there is a systemic ground problem in the house.

Here is a site about home generators with a fair amount of background information that, while not directly relevant, discusses different grounding configurations and their implications on operation and safety. The site operator was very helpful in helping me diagnose via email an issue I was having with my generator (not furnace related).

Home generator installation

I installed an 8 foot 5/8 inch ground rod at the generator and connected it with a #6 copper wire. The house grounding system was not checked. I will check that on Mon. along with all other things I can think of. Thanks for your response KeepitSimpleStupid. Thanks for the link bkspero, I will read it and see if there is any info that might be useful.

Something doesn't sound right. 50 A, #6 , CMA 26244, K 12.9 Copper, 120 V, Voltage drop is
4.1% which is higher than the 3% without de-rating etc. I did use 120 rather than 240 because a neutral is involved.

At 0.8*70 A and 120 V, the drop is 4.6%

I'd suggest checking the voltage drop as well.

#3 AWG copper gives you a 2.7 % drop IF all the loads (56 Amps, 0.8 of 70 A are on one leg of the 240. I think you should have run #3 copper.

56*120 = 6720 Watts

10 KW/120 = 133 A. If the generator is capable of 16 KW continuous, then you should size for 133 A, but you have a 70 Amp breaker. 70 A continuous then you would need #2 wire. 70*120 = 8400 Watts. That isn't 16 KW either at 120 V. You really need to size the wire at 70*1.25 or 87.5 AMPs which is really #1 wire.

16 KW symmetrically loaded would be 66.6 A. The next breaker size would be 70 A.

If the generator were symmetrically loaded, it would be 41 Amps on L1 and L2 and 0 amps on the neutral for the furnace, but the furnace probably has some 120 V.

I think your wire is too small.

Y

I didn't quite word the last post right. After I re-read it, this is what I meant. I used a #6 wire to ground the unit to the grounding rod. I do agree with what you put down though, KeepitSimpleStupid except with the 10kW/120. The unit is a 10kW/240V. Sorry about the mix-up on the clarity of the ground wire, my fault. Thanks. I didn't get to the house today, I will be there tomorrow morning.

Your right. 10 KW/120 isn't 133, but 16 KW/120 is 133. I didn't go back and change the numbers. I initially made a mistake and had to re-calculate and I missed that one. Good catch. Which means you understood it.

I really meant 120, not 240 because I was trying to show that capability of 16 KW cannot be all on L1 and none on L2. The 70 A breaker on the generator proves this.

Voltage drops when doing a 240 4-wire system must use 120 V as the voltage. A 240 volt 3-wire system can get away with using 240 volts when doing voltage drop calculations. Hopefully, this makes sense.

Did you run #6 wire for L1, L2, N, Ground and the ground rod. This is what I assumed.

Yes, #6 for L1, L2, N. I am going to the house in the A.M. I understand now what you were saying after I re-read your post. This thing is driving me nuts! I know I will get it figured out. Thanks and any info on any tests you can think of would help. Just to double check what I am going to do. Thanks again I'll check this in th am before I head out .

I can now run the furnace, but the main power for the generator (circuit breaker) will not shut down the generator. I have turned off every breaker in both boxes, turned off the main in the original panel (the main for the generator is in this box) but I still have power to the generator (it still runs). I get no voltage reading across the lugs on the main generator breaker, I get 97V from lug to ground. And 107V from either T1 or T2 to either T1 or T2 main lugs in the generator panel. I hope you can understand this. Any ideas? I switched the wires in the main breaker for the generator. But this problem was discovered as soon as I started working on the generator. Thanks

Now I'm having a hard time understanding your comments.

First: Auto or manual transfer switch?

Second: Any links to drawings/schematics online?

Third: Generator breakers will likely NOT cause the generator to shut down. These are on the AC side and not the control side. The control side will be the battery side. AC power may only control the charger.

There is probably a switch that has designations of off/on/auto. In off, the generator is off. In on, the generator is on and in auto, the generator starts when utility power fails. When utility power resumes, the generator may not stop right away.

The voltages don't seem to be in tolerance.

Could those voltages your measuring be control voltages and not the output voltage of the generator. The generator's frequency is controlled by RPM. The output is controlled by other windings.

Go slower.

Sorry about not being more clear. I do not mean to insult you intelligence, so Please do not take any offense to this. I am going to explain this in as detailed as I can so that it is clear. This is a Guardian (generac) standby generator with an automatic transfer switch (ATS), a couple of links to try (one is a pdf)

GUARDIAN 16kW

http://www.guardiangenerators.com/pu...0174210SBY.pdf

On this one (pdf) on the last page you have a schematic of the wiring installation. If you look at the panel that is the 100A or 200A house main service you can see the generator main breaker (40A or 70A 2-pole circuit breaker) is the one on the lower left. This will completely disable the generator (no power). On the right side is the generator breakers that are transferred over to the main panel. The 70A breaker is in the main panel to monitor the power from the power company. When the power is removed from the house panel (power outage, shutting off the main) the sensors in the generator panel acknowledges the power loss and in turn starts the generator. If you turn the 70A breaker off, it will turn off the sensors in the generator panel, and the generator will not start. I removed the breaker and the generator continued to run. This should not happen. I have installed two other generators and know this is true. The generator does have an auto/off/manual switch and it is in the auto position. I read the voltage from the 70A breaker to the lugs just above the breakers in the generator panel (see picture in pdf). NL voltage is 249V which is within specifications.I hope this will explain more in detail about the connection and what I am trying to say. Thanks for your response.